1. Field of the Invention
The present invention generally relates to a solid-state imaging device, e.g., a CCD (charge-coupled device) image sensor or the like. More specifically, the present invention is directed to a charge-coupled device having a plurality of color filters, and a plurality of on-chip condenser lenses whose dimensions and curvature values are different from each other based upon thicknesses of the color filters.
2. Description of the Prior Art
A CCD solid-state imaging device, specifically a color solid-state imaging device is constructed as follows. That is, as illustrated in FIG. 1, sensor portions 2 functioning as the respective pixels, namely photodiodes functioning as light sensitive portions are formed on the surface of a semiconductor substrate 1, a color filter 4 constructed of chromatic filter components is fabricated via a protection film 3 on the overall surface of the semiconductor substrate 1 containing the sensor portions 2, and microscopic (small) condenser lenses 5 for increasing sensitivities of the CCD solid-state imaging elements or sensor portions 2 are formed on the respective chromatic filter components, respectively. Insulating films 7 are formed on the surface of semiconductor substrate 1 between adjacent sensor portions 2.
The color filter 4 is manufactured, as shown in, for example, FIG. 2, in such a manner that a pattern formed of green (G), cyan (Cy), yellow (Ye), and magenta (Mg) chromatic filter components 4G, 4Cy, 4Ye and 4Mg is repeated. Each small condenser lens 5 is made of, for instance, a photoresist film.
As previously explained, the above-described method for forming the small condenser lenses 5 on the sensor portions 2 has been conventionally employed so as to increase the sensitivities of the CCD solid-state imaging element. In this case, there is a problem in a product whose CCD solid-state imaging element employs the color filter 4. Namely, sensitivity increasing rates for the respective pixels are different from each other, depending upon the patterns of the chromatic filter components formed on the sensor portions 2.
A change in a sensitivity increasing rate is also caused by the thickness of the protection film 3 mounted on the photodiodes 2 functioning as the light sensitive portions and also the thicknesses of the respective chromatic filter components 4G, 4Cy, 4Ye and 4Mg. When, for instance, a green dye layer (i.e., the green filter component 4G) is formed by a dye of an additive complementary color, this green dye layer is formed by overlapping a cyan dye layer (namely, the cyan filter component 4Cy) with a yellow dye layer (namely, the yellow filter component 4Ye). As a consequence, a thickness t of the green dye layer 4G is different from thicknesses t.sub.2 and t.sub.3 of the cyan dye layer 4Cy and yellow dye layer 4Ye. Also, as to the cyan dye layer and the yellow dye layer, the thicknesses t.sub.2 and t.sub.3 thereof are separately selected to be proper values, taking account of color reproducibilities and appearances of false signals. Accordingly, the thicknesses t.sub.1, t.sub.2, t.sub.3 and t.sub.4 of the respective dye layers, i.e., respective chromatic filter components 4G, 4Cy, 4Ye, and 4Mg fabricated on the respective sensor portions of the imaging device, represent different values, depending upon the pattern of the color filter 4.
In case that the thicknesses of the color filter components (dye layers) differ from each other, the light converging rate achieved when the small condenser lenses 5 are provided is varied due to refractive index and the like. As a result, the increasing rate of sensitivity achieved when the small condenser lenses 5 are provided to that when no small condenser lenses 5 are employed represents different values with respect to the pixels, depending upon the pattern of the color filter 4.
In other words, as indicated in FIG. 3, the sensitivity increasing rate of the cyan dye layer 4Cy represents the highest value, and then the sensitivity increasing rates of the magenta, yellow, and green dye layers 4Mg, 4Ye, and 4G are successively lowered. It is assumed in this figure that magnification achieved when no lens if employed is 1.0.
If the sensitivity increasing rates would be different from each other, then the false signal when the small condenser lenses are provided will appear in a different manner, as compared with the appearance of the false signal when no small condenser lenses are employed, for instance, in order to perform the signal processing operation, thereby separating the luminance signal from the color signal in case of the CCD solid-state imaging device with employment of the color filters 4 belonging to the additive complementary color system. Furthermore, color reproducibility would be changed due to a similar reason to the above-explained reason.
To make a CCD solid-state imaging device compact in size without deteriorating its resolution, since an area of a light sensitive portion thereof is necessarily reduced, the sensitivity of the imaging device is tried to be increased by increasing the converging rate of the small condenser lenses 5 formed on the sensor portions 2. As a consequence, such differences in the sensitivity increasing rates for the respective pixels caused by the small condenser lenses may greatly give adverse influences to chromatic characteristic of the color CCD solid-state imaging device when the color CCD solid-state imaging apparatus is made compact in size. Also, these sensitivity increasing rates may constitute important factors to determine these values.